The invention relates to a device for folding over the edge of a dressing or packing drawn onto a cylinder of a printing or varnishing machine, including an edge folding element and a mechanism or linkage for adjusting the edge folding element towards and away from the cylinder.
A printing plate is drawn onto a plate cylinder in a number of steps. Initially, the leading edge of the plate is firmly clamped in a clamping device applied or fitted to the cylinder. This is followed by actually mounting the plate, wherein the cylinder rotates and a pressure roller rolls on the plate in a direction towards the trailing edge thereof. In order to be able to clamp the trailing edge firmly in a further clamping device applied or fitted to the cylinder, it is necessary to bend the plate around an edge of a channel or gap formed in the cylinder and, in this regard, to press the trailing edge onto a contact surface of the clamping device.
An edge folding device described in the published German Patent Document DE 42 14 207 C1 can be used for this purpose, for example, an edge folding strip or bar thereof being pushed forward by two pneumatic cylinders into a position provided for folding over the edge of the printing plate. Rockers are hinge-mounted on or articulatingly connected to piston rods of the pneumatic cylinders, free ends of the rockers having rollers which press against the edge folding strip in order to displace the latter from the initial position thereof.
As a rule, printing or varnishing plates are very stiff, so that the trailing edge of the plate projecting beyond the edge of the channel or cylinder gap, because of the inherent elasticity of the trailing plate edge, exerts a force acting upon the edge folding strip which forces the latter away from the cylinder until the trailing edge has been firmly clamped into the clamping device.
With regard to preventing the edge folding strip from being forced away by the trailing edge, and intercepting the action of a force exerted by the trailing edge, the edge folding device described in the German patent document is not constructed very advantageously, because during the firm clamping of the trailing edge, the pneumatic cylinders have to continue to have compressed air applied thereto, in order to counteract the force exerted by the trailing edge.
A further disadvantage of the aforedescribed edge folding device is that it cannot be re-equipped or retrofitted for manual actuation. Assuming that, instead of the pneumatic cylinders, an operator were to actuate the rocker, the operator would have to hold the rocker continuously in a rocker position pivoted towards the cylinder until the trailing edge were fully firmly clamped, which would be very awkward. In addition, the operator holding the rocker firmly would not have both hands free to clamp the trailing edge firmly in the clamping device.
Although, on the one hand, there is a trend towards the increasing automation of functions of printing machines, on the other hand, there is also a high demand for printing or varnishing machines which are simple in terms of construction and therefore cost-effective, with a low degree of automation. In the case of these simply constructed machines, the omission of actuating drives, such as the aforementioned pneumatic cylinders for the edge folding strip, and providing instead the capability of operating the machines manually are desirable.
A device described in the published German Patent Document DE 198 01 844 A1 for inserting an edge of a plate exemplifies further prior art. This device does not have a pivotable edge folding element but a slide for inserting the plate into a clamping device, and is much too complicated for simply constructed machines.
It is accordingly an object of the invention, therefore, to provide an edge folding device which is particularly suitable for manual actuation.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a device for folding over an edge of a dressing or packing drawn on a cylinder of a printing or varnishing machine, including an edge folding element, and comprising a linkage or mechanism for moving the edge folding element towards and away from the cylinder, the linkage being constructed as a self-locking mechanism.
In accordance with another feature of the invention, the linkage is constructed as a four-bar linkage with a coupler.
In accordance with a further feature of the invention, the linkage is constructed in a manner similar to a four swivel-joint chain.
In accordance with an added feature of the invention, the coupler forms an element in the linkage which is shortest in terms of central spacings between swivel joints of the linkage.
In accordance with an additional feature of the invention, the coupler has an articulating knee, which is displaceable into an overstretched position, wherein the linkage acts in a self-locking manner.
In accordance with yet another feature of the invention, the knee is formed by the coupler together with a drive rocker arm of the linkage.
In accordance with yet a further feature of the invention, the drive rocker arm is of double-armed construction, including a first lever arm whereon a handle is disposed, and a second lever arm to which the coupler is linked.
In accordance with yet an added feature of the invention, the linkage includes a driven rocker arm disposed so as to be swivellable about a swivel joint and having thereon a stop for the coupler, the stop serving to block overstretching of the knee beyond the overstretched position.
In accordance with yet an additional feature of the invention, the edge folding element is disposed on a lever arm of the driven rocker arm, and the coupler is linked to the lever arm, between the swivel joint and the edge folding element.
In accordance with still another feature of the invention, the device includes a stop for blocking movement of the linkage, the stop being disposed on an element of the linkage.
In accordance with still a further feature of the invention, the device includes a stop for blocking movement of the linkage, the stop being disposed on an element of the linkage located adjacent to the coupler.
In accordance with still an added feature of the invention, the linkage has a swivel joint for swivelling the edge folding element about the swivel joint and towards and away from the cylinder.
In accordance with a concomitant aspect of the invention, there is provided a printing or varnishing machine having a device for folding over an edge of a dressing or packing drawn on a cylinder of the machine, including an edge folding element, and comprising a linkage for moving the edge folding element towards and away from the cylinder, the linkage being constructed as a self-locking mechanism.
Thus, in the edge folding device according to the invention, the mechanism or linkage for moving the edge folding element is constructed as a self-locking mechanism.
This construction of the mechanism is advantageous with regard to the ability to operate the edge folding device manually, because the operator has both hands free to clamp a trailing edge of the dressing or packing drawn on firmly in a clamping device, after the edge folding element has been displaced towards the cylinder into an edge folding position and, after reaching a specific position of the mechanism, the automatic, positively locking blocking thereof with respect to a force acting on the edge folding element has become effective.
The automatically blocking construction of the mechanism or linkage is also advantageous with regard to the equally possible motor-driven movement of the edge folding element into the edge folding position. For example, the application of compressed air to a pneumatic cylinder acting as an actuating motor for moving the edge folding element can be switched off after the self-locking of the mechanism or linkage in the given position thereof has become effective.
In connection with the invention, xe2x80x9cedge foldingxe2x80x9d is understood to mean bending over a dressing or packing drawn onto the cylinder, in particular where the dressing or packing is bent over in a direction towards a cylinder channel or gap formed in the cylinder and towards a clamping device in the cylinder channel or gap and, in particular, where the position of a bending point of the dressing or packing drawn on is predefined during the folding action by an edge of the cylinder channel or gap, beyond which the drawn-on dressing or packing projects.
In an embodiment which is advantageous with regard to minimizing the number of parts, the self-locking mechanism or linkage is constructed as a coupler mechanism or linkage, which comprises four joints and only four mechanism elements connected to one another by the joints. It is preferable for a frame, a drive lever, a coupler and a driven lever to form the four mechanism elements connected to one another by joints
In a further embodiment, which is advantageous with regard to cost-effective production of the joints, each of the four joints is a pivot or swivel joint. Two of the pivots can be arranged as stationary pivots for mounting the levers in the frame, while the two other pivots can serve to connect the coupler to the levers.
In a further embodiment, which is advantageous with regard to constructing the coupler mechanism as a double-armed rocker, the center spacing between the two pivots serving to attach the coupler to the two levers is shorter than the other three center spacings. They are the center spacing between those pivots or swivel joints which serve to attach the drive lever to the frame and to the coupler, the center spacing between those pivots or swivel joints which serve to attach the driven lever to the coupler and to the frame, and the center spacing between those stationary pivots or swivel joints which serve to attach the levers to the frame. The frame is preferably the longest element in the coupler mechanism, the center spacing of the stationary pivots serving to attach the levers to the frame being greater than that of the other three aforementioned center spacings.
In a further embodiment, which is advantageous with regard to single-handed operation, a pivot and two elements of the coupler mechanism or linkage that are connected to one another by this pivot form a jointed knee which, in an angular position of the two mechanism elements relative to one another which deviates from a straight line, together with a stop which one of the elements of the mechanism strikes, effects the self-locking of the mechanism.
In a kinematically advantageous further embodiment, the coupler of the coupler mechanism or linkage is the one element of the mechanism or linkage of the knee, and the drive lever which serves to introduce force for displacing the mechanism or linkage is the other element of the mechanism or linkage of the knee.
In a further embodiment, which is advantageous with regard to simple operability of the device, the drive lever is constructed as a rocker which, at one end thereof is connected to the coupler via the pivot or swivel joint, and an operating element is arranged at the free other end thereof.
In a further embodiment, which is advantageous with regard to secure self-locking of the mechanism or linkage, the driven lever is provided with a stop, which the coupler strikes in the overstretched position and which, together with the knee effects the self-locking of the mechanism or linkage.
In a further embodiment, which is advantageous with regard to the ability of the edge folding element to pivot or swivel about a pivoting or swivel axis which is offset relative to a pressure roller, one end of the driven lever is connected to the coupler via a pivot or swivel joint and carries the edge folding element at the free other end thereof. It is therefore possible for separate mountings to be provided for the pressure roller serving to roll the dressing or packing drawn onto the cylinder, and the edge folding element serving to bend the dressing or packing drawn on after it has been rolled on.
The edge folding device according to the invention is preferably assigned to the plate cylinder of a rotary printing machine in order to assist the firm clamping of a printing or varnishing plate. The rotary printing machine may comprise a number of offset printing units and a varnishing unit, constituent parts of which are the plate cylinder and the edge folding device.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an edge folding device, it is nevertheless not intended to be limited to the details shown, since various. modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: